High density ployethylene, polyvinyl chloride, polyethylene terephthalate, and polypropylene are the resins most used for bottle applications.

Typical industrial blow molding applications includes fuel and oil tanks, industrial drums and containers, shipping containers, labware, recreational vehicles, lawn-and-garden equipment, carrying cases,and toys.

Here are the various types of blow molding and their applications:

Extrusion Blow Molding

• Most widely used blow molding technique today.
• This process can be used to form thermoplastics into a wide range of hollow, thin-walled, one-piece parts.
• An extruder melts the plastic and pushes it through a die to produce a parsion or tube.
• A mold with the desired cavity shape closes around the parison, pinching shut one end and clamping the other around a blow pin. The parsion is cut from the extruder simultaneously.
• Air from the blow pin enter the parison and the parison expands or stretches into the shape of the cavity.
• Water passes through the mold and cools the plastic until it will hold its shape.
• The air pressure is then released, the mold opens, and the molded part is ejected.
• Products: bottles, gasoline tanks, toys, business machine panels.

Injection Blow Molding

• This process is commonly used for blow molding bottles.
• It can produce bottles which are as large as 5 gal in capacity.
• Products: mostly used for small, irregularly shaped bottles and hollow industrial parts that would be difficult to mold using the extrusion-blow molding process.

Blow Molding with Engineering Resins

• It is most suitable for large parts that need stiffness and some complexity.
• Plastic replacements for sheet-metal covers and enclosures for products such as computers.
• Handles modest volumes.
• Tooling is faster and less costly than that of injection molding and structural-foam processing alternatives.
• Engineering resins used for this process include modified polyphenylene ether/polyphenylene oxide which contribute important thermal, flame, and modulus properties
• Further stiffening can be achieved by using ribbing, foam filling, tackoffs, or inserted stiffeners such as metal rods or wood.
• Products: computers and business equipment

These are listed to be a starting point for designers. Each plastic part is different so some of these rules might not apply.

Being creative is knowing when and where to "bend" the rules...

Check here for a blow molding illustration.

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